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Well-lubricated bicycle wheel problem

  1. Feb 5, 2009 #1
    1. The problem statement, all variables and given/known data
    A well-lubricated bicycle wheel spins a long time before stopping. Suppose a wheel initially rotating at 170 rpm takes 70 s to stop.

    A)If the angular acceleration is constant, how many revolutions does the wheel make while stopping?


    2. Relevant equations
    i used circular motion kinematics equations.


    3. The attempt at a solution
    i changed 170 rpm to 17.80 rad/s. then i used wf=wi+(alpha)(delta)t
    wf=17.80 rad/s + (0-70s) = -52.2 rad/s^2
    i used (theta)F= (theta)i + wi (delta)t +1/2 ((alpha)(delta)t)^2

    i think i used the right equations but when i solve for wf i get -581 rad.... don't know if that's the right answer.

    i'd greatly appreciate the help :)
     
  2. jcsd
  3. Feb 5, 2009 #2
    I think you are making this unnecessarily complex.

    If the wheel starts at 170rpm at T=0 and is at 0rpm at T=70 and we know the deceleration is constant, what rotational speed was it turning at at T=35?
    If we know that what can we do with that information?

    Beware of rpm and revs per second!
     
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